Ghosting rears its head... SLT

I have an A55 that has been a very good camera for me. However, in the past week I've seen 5 or so images out of about 75 that have ghosting. I don't think I've had 5 ghosting images in the past 1500 shots before this.

Couple things I've thought of that may contribute:

1. I think 3/5 were shot by my wife whom may not have a steady hand (although her limited number of shots didn't have ghosting before) and one I shot was a "from the hip" fast frame and shoot.

2. There were probably at least 3 of them shot w/ Superior Auto (just begun using this and was surprised it worked so well).

3. Humidity? I was in Washington DC and it was hot and humid--but I didn't have he problem in several trips to Hawaii which was humid but not as hot--anyway vapor on mirror??
4. Could the mirror need cleaning? Looks pretty clean...

Any other remedies?
Any ideas why?

Unfortunately, I erased each image when I noticed the ghosting not expecting to see more so I can't pull up the image parameters. Bummer.